[gl4java-usergroup] GLEventListener

[Combe, C. <C....@na...>]

Sorry for cluttering up the mailing list with what has turned into a bit of
a monologue.

I know the current recomendation is to use GLEventListener and not the
subclassing model, but the thing is i'm wanting to control when the canvas
is redrawn, not just have it redraw every so often. So, what I currently
have is a thread that spends most of its time outside my GLCanvas subclass
and then at the end of a cycle goes into that subclass and does
gljMakeCurrent(), draws, then does gljFree(). Given that this is how my
program works is there an advantage in changing to the GLEventListener
model? If i did change, should I still be using the makeCurrent/Free calls?
thanks,
colin

-----Original Message-----
From: Combe, Colin [mailto:C....@na...]
Sent: 17 December 2002 16:21
To: gl4...@li...
Subject: RE: [gl4java-usergroup] confused by reshape


OK, i wasn't managing my GLContext correctly. Maybe I should change to using
the EventListener way rather than the subclassing way. 

This is all about using gljMakeCurrent() and gljFree() to ensure that only
one thread is trying to issue gl commands at any time - right?

Do all commands that start glj. , gl. or glu. need to be between
gljMakeCurrent() and gljFree()? I notice people don't seem to put
instructions in their init() or reshape() methods between these commands -
why is this?. If you were 100% certain that only one Thread would call GL
commands could you miss the commands out (this is just out of interest, its
not something I want to do) ?

Is a thread blocked until gljMakeCurrent() suceeds? If not, and
gljMakeCurrent() fails do the commands just not happen?  

any advice about how to deal with multiple threads interacting with one
canvas will be most welcome,
cheers,
col

-----Original Message-----
From: Combe, Colin [mailto:C....@na...]
Sent: 17 December 2002 12:52
To: gl4...@li...
Subject: [gl4java-usergroup] confused by reshape


Hi

I'm a bit confused by the reshape() method. I've got a button, in the frame
that contains my subclass of GLCanvas, which I use to swap between a 2D and
a 3D view. Depending on whether the canvas attribute 'flat' is true or false
the button calls either goFlat() or go3D(). Here a code extract from my
canvas class :

    public void reshape(int width, int height)
    {
        if (flat) goFlat();
        else go3D();
    }
    public void goFlat()
    {
      //not sure if you need to change to projection matrix before call to
gluOrtho2D  
	gl.glMatrixMode(GL_PROJECTION);
        //Reset The Projection Matrix
        gl.glLoadIdentity();
        glu.gluOrtho2D(0, ((landWidth * 2) + 1), ((landWidth * 2) + 1), 0);
        gl.glMatrixMode(GL_MODELVIEW);
        gl.glViewport(0, 0, this.getWidth(), this.getHeight());
        flat = true;
    }
    public void go3D()
    {
        //Select The Projection Matrix
        gl.glMatrixMode(GL_PROJECTION);
        //Reset The Projection Matrix
        gl.glLoadIdentity();
        glu.gluPerspective(viewAngle, (float)getSize().width /
(float)getSize().height, NPDist, 4500.0f);
        gl.glMatrixMode(GL_MODELVIEW);
        gl.glViewport(0, 0, this.getWidth(), this.getHeight());
        flat = false;
    }

The method that draws to the canvas does different things depending on the
state of the 'flat' attribute. This sort of works but you need to resize the
window after changing between 2D and 3D mode - this doesn't make sense to me
as (it looks like) all the reshape() method does is call goFlat() or go3D(),
which were called when the button was pressed. 
?
cheers,
colin


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_______________________________________________
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